Expendible gun assembly for perforating wells



0d. 1965 I. J. MOCULLOUGH ETAL 3,211,093

EXPENDIBLE GUN ASSEMBLY FOR PERFORATING WELLS Filed Aug. 10, 1962 4 Sheets-Sheet 1 W////a//'7 6? Jweefman INVENTORS Q L TL 1955 I. J. MGCULLOUGH ETAL 3,211,093

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EXPENDIBLE GUN ASSEMBLY FOR PERFORATING WELLS Filed Aug. 10, 1962 4 Sheets-Sheet I5 Arra/PMsy Oct. 12, 1965 1, J. MOCULLOUGH ETAL 3,211,093

EXPENDIBLE GUN ASSEMBLY FOR PERFORATING WELLS Filed Aug. 10, 1952 4 Sheets-Sheet 4 I [/a L/. MC (QM/009% Of/J 1/ McCu//00g/i W////0/77 (3 Jweefman 42 INVENTORS 7 5 I) BY flaw;

ATTORNEY United States Patent O 3,211,093 EXPENDIBLE GUN ASSEMBLY FOR PERFORATING WELLS Ira J. McCullough, McCullough Tool Company, 5820 S. Alameda St., Los Angeles 58, Calif., and Otis J. McCullough and William G. Sweetman, McCullough Tool Company, P.O. Box 2575, Houston, Tex.

Filed Aug. 10, 1962, Ser. No. 216,112 5 Claims. (Cl. 10220) This invention relates to an expendible gun assembly for use in perforating in wells such as oil and gas Wells, and more particularly to an improved expendible glassencased explosive perforating unit, and a gun assembly comprising a number of such units connected by glass couplings and supported in a sling-type carrier.

The use of expendi-ble well perforating devices employing shaped charges of explosives as the perforating elements have been widely adopted in the oil industry, however, the use of such perforators has been accompanied by the problem of the deposition of too much so-called junk, that is, the metal debris resulting from the usual metal casings enclosing the perforating units and the various types of metal carriers conventionally employed for supporting and lowering the strings of perforating units into the well. Such debris frequently interferes with the production of oil and gas from the well by plugging flow valves, pumps, gas traps and wellheads. While producers suffer large expenses bailing and swabbing endeavoring to remove the debris after perforating. Very often it is impossible to run clean-out tools into a well after perforating due to high pressures which have been opened into the well through the perforations.

Many wells in accordance with current slim-hole completion and production practices employ quite small diameter pipe as casing and production strings, often only 2 inch or 2 /2 inch tubing, and even smaller sizes, which is cemented in place in the Well bore. Since the casing bore in such a Well is quite small, the employment of perforating devices which produce metallic junk or debris will fill up substantial amount of the casing or of the tubing, and seriously interfere with the production of oil and gas from the well, especially when, as is often the case, a perforating assembly or gun usually comprise a substantial number, and very often hundreds, of perforating units in one zone in a well.

In an eifort to overcome these various disadvantages of more conventional perforators, some perforating units have been encased in glass, as disclosed in US. Patent No. 2,629,325 to W. G. Sweetman, and these have been mounted in recoverable carriers constructed of relatively thin strip metal, as disclosed in US. Patent No. 2,756,677 to I. J. McCullough. While this expedient has constituted a substantial improvement in this art, the removal of the carrier after use has presented some problems. U.S. Patent No. 3,040,659 to O. I. McCullough has provided a perforator comprising a series of self-contained perforating units which are also self-supporting in that they may be directly connected to one another by a coupling arrangement to form strings of any desired length. This construction has very successfully rnet the problem of space limitation in providing powerful perforating units dimensioned for use in small bore tubing, but the problem of excessive debris, while greatly reduced by the elimination of a separate carrier, has, nevertheless, continued to cause some difficulty in perforating operations.

The present invention, therefore, has for its principal object, the provision of an improved form of perforating device which eliminates or greatly obviates the aforementioned disadvantages of earlier devices, by providing a highly eificient perforating device particularly dimensioned 3,211,093 Patented Oct. 12, 1965 for use in small bore tubing and producing a minimal amount of metallic debris.

In accordance with one embodiment of this invention, there is provided a perforating device comprising a series of self-contained shaped charge perforating units each enclosed in a casing completely constructed of glass and strung together in strings of any desired length by means of a unique connector arrangement comprising a wire sling extending lengthwise along opposite sides of the string of charges and passing through a series of constricting collars constructed of glass. One collar is disposed about the adjacent abutting end portions of each pair of perforating units and the wire sling is threaded through the collars and over the opposite sides of the perforating units. When the ends of the wire sling are drawn taut, the constrictive action of the collars serves to draw the perforating units together tightly in end-to-end relation to complete the gun assembly. The tight end-to-end engagement thus effected between the perforating units serves to establish etfective successive transmission of detonating shock throughout the entire length of the string. Since the casings for the perforating units and the constricting collars are of glass, the only metallic debris resulting from setting off of the perforating device will be that formed from the relatively thin wire sling, it will be evi-' dent that the present device will practically eliminate the plugging problem encountered with more conventional devices.

Another object of this invention is the provision of a glass-encased shaped-charge perforating unit embodying several novel features of construction providing a highly eflicient self-contained perforator for use in multiple unit strings particularly adapted for running in small diameter Well tubing.

Other and more specific objects and advantages of this invention will become more readily apparent from the following detailed description when read in conjunction with the accompanying drawing which illustrates useful embodiments and modifications in accordance with this invention.

In the drawing:

FIG. 1 is an elevational view of a perforating device embodying this invention;

FIGS. 2A, 2B, and 2C, together, comprise an elevational view, generally similar to FIG. 1 but in larger scale, having portions thereof broken away to illustrate the details of the device;

FIG. 3 is a perspective view of one of the elements of the device;

FIGS. 4A and 4B, together, comprise a view generally similar to FIGS. 2A, 2B and 2C, but viewed in a position turned from that of the latter figs;

FIG. 5 is a fragmentary view of a portion of a string of perforating units showing an arrangement for varying the spacing between the units;

FIG. 6 is a cross-sectional view taken along line 66 of FIG. 5; and

FIG. 7 is a longitudinal cross-sectional view of a modified form of a perforating unit.

As seen in FIG. 1, the gun assembly comprises a plurality of perforating units, each designated generally by the numeral 10, strung together in end-to-end relation in a sling-type carrier, designated generally by the numeral 11, which also supports 'a bottom firing head, designated generally by the numeral 12, in detonating relation to the lower end of the string of charges. The upper end of carrier 11 is secured by means of a hanger sub 13 to weight bars or other generally conventional rope socket 14, by which the perforating device is lowered into a well on a wire rope or cable 15, the latter carrying the conductor 16 through which firing current may be transmitted from the surface to the firing head.

Each of the perforating units comprises a hollow casing 20 having a generally ovoid or oblate spheroidal shape and having integral end portions 21, the exteriors of which are of generally cylindrical shape and substantially smaller in diameter than the main body of the easing. End portions 21 terminate in end walls 22 closing the ends of the casing. End walls 22 are substantially flat on their outer faces while their inner faces are provided with axial sockets or recesses 23, the outer ends of which are closed by relatively thin sections 24 of the end walls. The thickness of end sections 24 is dimensioned to effectively transmit detonating shock from either face thereof to the other. The change in shape of end portions 21 and their reduction in diameter with respect to the main body of the casing defines the external annular shoulder 25 at the base of each end portion. Casing 20 is split transversely at its mid-point to form two symmetrical half-sections which are secured together at 26 by means of any suitable industrial adhesive when the unit is assembled. Casing 20 is provided on opposite sides thereof with longitudinally extending grooves 27 of a depth to accommodate the carrier sling and an electrical conductor wire, as will be subsequently described.

An explosive perforating charge, designated generally by the numeral 30, is encased by casing 20 and is of any generally conventional shaped or hollow charge type, comprising, a generally cylindrical body 31 of any high explosive material commonly employed for well perforating, formed to provide a generally conical hollow 32 in one end thereof, and the opposite end 31a being rounded, as shown (FIG. 6). The charge is seated in the interior of casing 20 at the mid-portion thereof with hollow 32 facing to the side of the casing at an angle of 90 with respect to the grooves 27, the hollowed end being seated against an internal shoulder 39 provided in the interior of casing 20. A liner 33, of well-known form and construction adapted to increase the penetrating effect of the explosive, is seated in hollow 32. Explosive 31 may be encased in a like-shaped capsule 34, which may be constructed of lead or plastic, or any other suitable material; or if desired, the body of explosive may be molded or pressed to the desired shape and size and employed with out the encasing capsule.

A detonating explosive fuze 35 of elongate, flexible form, is arranged interiorly of casing 20 to extend generally longitudinally thereof, the intermediate portion of the fuze element being disposed in detonating contact with the end 31a of the explosive body 31. The opposite end portions of fuze element 35 extend into recesses 23 at the opposite ends of the casing and into direct contact with the inner faces of sections 24 of Walls 22. Each of the ends of fuze element 35 may be provided with a small body of booster explosive 36 which is secured to the end of the fuze element by an encasing clip or ferrule 37. A small body 38 of a booster explosive may be positioned at the point of contact between fuze element 35 and end 31a of explosive charge 31. These several booster charges serve to assure high-order detonation throughout the explosive system of the perforating unit. Fuze element 35 may be conventional Primacord or a similar flexible detonating fuze.

To form the gun structure illustrated in FIG. 1, a plurality of the perforating units 10 will be connected together to form a string of a length to include any desired number of units. The units are connected together by inserting the end portions 21 of adjacent units into the opposite ends of a collar 40 having a bore 41 which fits with a small degree of looseness about the end portions, the length of the collar being slightly less than the overall length of the two abutting end portions 21. Sling 11, which is preferably formed from a single length of flexible wire, is employed to secure the several perforating units together in a unified string. In its final form sling 11 constitutes a generally U-shaped structure comprising the arm portions 42a and 42b connected by the bottom portion 420 and is applied by threading the opposite arm portions 42a and 42b upwardly through the grooves 27 along opposite sides of the string of units, the wire passing through the bores of the successive collars 40 and being drawn upwardly by any suitable means until bottom portion 420 engages beneath and around firing head 12, which will be described in greater detail hereinafter. When the sling is in place about the string of charges, arm portions 42a and 42b will be drawn taut in the upward direction. As the diameter of bores 41 of collars 40 are made substantially less than the external diameter of casings 20, the collars will serve to constrict both arms of the sling wire so that as the upper ends are pulled tight, collars 40 will serve as fulcrums causing the perforating units to be drawn tightly together in abutting end-to-end relation. In drawing the arm portions of the sling tight, the ends thereof will be led through longitudinally extending holes 4343 provided in hanger sub 13 (FIG. 2A) and set screws 44 are screwed through the wall of the hanger sub to clamp the ends of the wire tightly against the walls of holes 43, thereby effectively securing the sling to the hanger sub. In mounting the perforating devices in the sling, firing head 12 will be inserted into the lowermost collar 40, which is positioned about lower end portion 21 of the lowermost ones of the perforating units 10. The firing head, which is preferably made of light, thin metal, such as aluminum, has a central core 45 from which a pair of ribs 46 extend outwardly in opposite directions, defining shoulders 47 which are adapted to abut against the lower end of the lowermost collar 40 when core 45 of the head is inserted into the bore of the collar, as best seen in FIG. 4B. A second pair of ribs 48 extend oppositely from core 45 intermediate the ribs 46 and are of greater length than ribs 46. Ribs 48 likewise have shoulders 49 adapted to abut the lower end of the lowermost collar 40. Ribs 48 are split longitudinally to form the channels 50 through which the sling is threaded in passing it around the lower end of the string of charges. Thus, when the ends of the sling are drawn taut, head 12 will be pulled tightly up against the lower end of the lowermost collar 40. Core 45 has an axial bore 51 adapted to receive an electrically fired detonating cap 52 (FIGS. 2C and 4B) which is secured in a manner to project from bore 51 into abutting engagement with end wall 22 of the lowermost perforating unit, being held in engagement by means of a wire clip 53 which extends transversely across the lower end of cap 52 and is secured on opposite sides thereof in openings 5454 provided in ribs 46, as best seen in FIG. 4B. An electrical conductor 16a is laid in groove 27 but extends only along one side of the string of perforating units, being threaded through the bores of the several collars 40. This conductor is connected to cap 52 and a ground wire 55 is secured by means of a screw 56, which is threaded into an opening 57 in one of the ribs 48- of the firing head to complete the electrical circuit to cap 52 (FIGS. 2C and 3). The upper end of conductor 16a is threaded through a bore 58 in hanger sub 13 and is connected at 59 to the main conductor lead 16, which leads to the surface through cable 15, and the other portions of the device above connector sub 13.

One of the important features of the present invention is that casings 20 and collars 40 are all constructed of glass. The glass is desirably high strength boro-silicate glass, such as that made by Corning Glass Works, Corning, N.Y., which, while having great compressive strength suflicient to withstand high hydrostatic pressures, will, upon being shattered, break down into extremely fine powder-like particles. Other types of glass may, of course, be employed, since, in general, any glass material will, on being shattered, break down into quite small particles which will cause no difiiculties in well pipes such as is occasioned by detritus produced by metallic structures commonly used in perforating operations.

The thickness of wall sections 24 will be made such as to afford ready transmission of the shock wave from one of the units to the next. In general, the thickness of wall sections 24 will be in the range of from about 0.05 to 0.10 inch, depending upon the type of glass and the pressure conditions to which the casings are to be subjected. In the case of the particular glass mentioned above, this wall thickness will be about 0.09 inch.

FIG. 7 illustrates a somewhat modified form of the perforating unit. It includes a casing 20a which is identical in external configuration with casing 20 but differs therefrom primarily in the internal form of the end portions. In the modification of FIG. 7, the bores of end portions 21a are shaped to provide generally hemispheric recesses 23a. The apex portion of recess 23a defines a thin end wall section 24a which, except for its hemispheric interior shape, corresponds generally in thickness at the center to end wall section 24 of the previously described embodiment, particularly in having the substantially flat external end face 22a, as previously described.

A centralizer or spacer element 57a having a hemispheric shape complementary to that of recess 23a is seated in the latter and secured to the walls thereof by a suitable industrial adhesive. Centralizer element 57a has an axial bore 58a extending therethrough to receive the end of fuze element 35 which, as in the previously described embodiment may be encased with a booster explosive pellet 36 by means of the ferrule 37. Centralizer element 57a is preferably constructed of glass, ceramic or other non-metallic readily frangible material which will shatter to a palpable powder upon explosion of explosive-shaped charge 30. The latter and fuze element 35 are identical in form and arrangement to the previously described embodiment.

In operation, the string of units secured together in the manner described, will be lowered into a well to a point at which perforation is to be effected. Electrical current will then be sent through conductors 16 and 16a to fire cap 52. The resulting detonation will be transmitted through the end wall sections 24 and thence through the several detonating fuzes 35, setting off the several explosive charges in succession in upwardly ascending order. The detonation of the several perforating charges will, of course, shatter the casings 20 and collars 40, as well as the wire comprising sling 11. The wire, which is a relatively thin, high strength wire, represents only a small amount of metal, and as a result, very little detritus or so-called metallic junk can accumulate in the well, even though quite a number of the perforating units may be employed in the string. The type of detritus so formed is easily washed from the Well by the flow of well fluids during the initial stages of production of the well.

In order to vary the spacing between the perforating units, where different spacing than that produced by directly abutting the units is desired, spacer units may be employed, these being illustrated in FIG. 5, wherein a spacer unit, designated generally by the numeral 60, is shown interposed between a pair of the units 10. Spacer unit 60 may be identical in construction to units 10, except that the perforating charge 30 is replaced by a pair of coaxially aligned explosive caps 61 which extend longitudinally through the interior of the casing, having their opposite ends seated in the respective recesses 23, the two caps being joined together by a short piece of Primacord 62. As a result, when a detonating Wave is transmitted through one of the perforating units abutting a spacer unit, this detonating wave will travel through the abutting wall sections 24 into the adjacent end of one of the caps 61 and thence through the fuze section 62 and the other cap 61 to the next adjacent unit 10. Any number of the spacing units 60 may be installed between perforating units to vary the spacing of the perforations, as may be desired by the operator.

Spacing units 60 may, if desired, be filled with lead shot 63 (FIG. 5) in order to increase the weight of the string, so that it may be more readily lowered through the fluids normally present in a pipe string or well bore into which it is run.

Ordinarily the over-all length of each of the units 10 will be about 3 inches so that if a series of units are assembled in a string without spacing units 60, perforations will be made in 3 inch centers or four to the foot. The spacing units being substantially identical in size to the perforating units, by interspersing one spacing unit between each pair of perforating units, perforations on 6 inch centers will result. Also, if only one perforation per foot is desired, three spacing units will be interposed between each pair of perforating units. It will be understood that spacing units 60 need not be identical in size or form with the perforating units but may be of any suitable dimensions, provided they are capable of effectively transmitting the detonating shock wave from one perforating unit to the next.

Instead of the bottom-firing arrangement illustrated herein, the string may be fired by placing the initiator cap in detonating contact with the topmost perforting unit. Both firing arrangements are commonly employed in well perforating devices using multiple shots.

The sealed self-contained perforating units, such as herein described, provide, in addition to the numerous other advantages previously noted, an important function depending upon the relation of the volume of air or free space in the casings to the amount of explosive in the charges 31. In the usual well perforating operation, the well pipe in which the perforator is run and which is to be perforated is generally filled with heavy mud or other liquid. Also, the Well pipe to be perforated will most often be tubing having an internal diameter of two inches or less. In such narrow confines and being submerged in liquid, the perforating units will, when fired, generate heavy shocks which, by reason of the incompressibility of the submerging liquid, will be transmitted to the pipe walls and to the cement sheath normally surrounding the pipe. As a result, in addition to the perforations effected by the shaped charges, the pipe may be ruptured and the cement sheath shattered or cracked over substantial length, permitting leakage of formation fluids through the thus broken cement, a condition which can be highly destructive to the Well.

With perforating units constructed according to this invention, the free space inside each casing 20 being filled with air, provides a compression chamber and a compressible medium which will absorb most of the undesirable shock produced by the detonation of the perforating charges and thereby obviate the undesirable results mentioned above.

To provide this shock-absorbing characteristic, the size of casings 20 may be selected so to provide a predetermined volume of free air space in relation to the mass of the explosive charge. In general, it is found that from about 5 cc. to about 10 cc. of free air space per gram of explosive will effectively reduce the collateral shock of the explosion to magnitudes which will not seriously damage the pipe or the surrounding cement sheath.

It will be understood that various changes and modifications may be made in the details of the illustrative embodiments of this invention within the scope of the appended claims without departing from the spirit of this invention.

What we. claim and desire to secure by Letters Patent is:

1. An expendible perforating gun assembly for use in wells, comprising, a plurality of self-contained perforating units, each unit including a hollow casing adapted for carrying a shaped explosive charge and having closed opposite end portions, and carrier means for supporting said units in an elongate string with said end portions in abutting end-to-end relation, said carrier'means including collar members separate from and surrounding each pair of abutting end portions, a generally U-shaped flexible wire sling having its bottom portion disposed in supporting relation beneath the lowermost one of said units and its arm portions threaded through the bores of said collar members and extending upwardly along opposite sides of said units, and means securing the upper ends of said arm portions in tension about said units, said casings and said collar members being constructed of glass.

2. A perforating gun assembly according to claim 1, including means mounted on said carrier for firing said charges from one end of said string.

3. An expendible perforating gun assembly for use in wells, comprising, a plurality of self-contained perforating units, each unit including a hollow casing adapted for carrying a shaped explosive charge, each of said units having closed opposite end portions of reduced diameter with respect to the intervening portion of the casing, and carrier means for supporting said units in an elongate string with said end portions in abutting end-to-end relation, said carrier means including a hanger member disposed above the uppermost one of said units, a generally U-shaped flexible wire sling depending from said hanger member, said sling having its bottom portion disposed in supporting relation between the lowermost one of said units and its arm portions extending upwardly along opposite sides of said units, means securing the upper ends of said arm portions to said hanger member in tension about the string of units, collar means separate from and slidably surrounding each pair of abutting end portions and the adjacent portions of said sling to secure said units to the sling, the internal diameter of said collar means being less than the external diameter of said intervening casing portions whereby to radially constrict said adja- 3 cent portions of said sling to increase the tensional force exerted by said sling to urge the abutting end portions of said units into tight engagement, said casings and said collar means being constructed of glass,

4. A perforating gun assembly according to claim 3, including means mounted on said carrier for firing said charges from one end of said string.

5. An expendible perforating gun assembly for use in wells, comprising, a plurality of self-contained perforating units, each unit including a hollow casing adapted for carrying a shaped explosive charge and having closed opposite end portions, and carrier means for supporting said units in an elongate string with said end portions in abutting end-to-end relation, said carrier means including collar members separate from and surrounding each pair of abutting end portions, a generally U-shaped flexible wire sling having its bottom portion disposed in supporting relation beneath the lowermost one of said units and its arm portions threaded through the bores of said collar members and extending upwardly along opposite sides of said units, and means securing the upper ends of said arm portions in tension about said units.

References Cited by the Examiner UNITED STATES PATENTS 2,708,408 5/55 Sweetman 102-20 2,761,383 9/56 Sweetman 102-20 2,819,673 1/58 Cecil et al 10220 2,927,534 3/60 Le Bus 10220 2,990,773 7/61 Toelke 102-20 2,990,774 7/61 Toelke 102-20 3,040,659 6/62 McCullough 102-20 SAMUEL FEINBERG, Primary Examiner. 

1. AN EXPENDIBLE PERFORATING GUN ASSEMBLY FOR USE IN WELLS, COMPRISING, A PLURALITY OF SELF-CONTAINED PERFORATING UNITS, EACH UNIT INCLUDING A HOLLOW CASING ADAPTED FOR CARRYING A SHAPED EXPLOSIVE CHARGE AND HAVING CLOSED OPPOSITE END PORTIONS, AND CARRIER MEANS FOR SUPPORTING SAID UNITS IN AN ELONGATE STRING WITH SAID END PORTIONS IN ABUTTING END-TO-END RELATION, SAID CARRIER MEANS INCLUDING COLLAR MEMBERS SEPARATE FROM AND SURROUNDING EACH PAIR OF ABUTTING END PORTIONS, A GENERALLY U-SHAPED FLEXIBLE WIRE SLING HAVING ITS BOTTOM PORTION DISPOSED IN SUPPORTING RELATION BENEATH THE LOWERMOST ONE OF SAID UNITS AND ITS ARM PORTIONS THREADED THROUGH THE BORES OF SAID COLLAR MEMBERS AND EXTENDING UPWARDLY ALONG OPPOSITE SIDES OF SAID UNITS, AND MEANS SECURING THE UPPER ENDS OF SAID ARM PORTIONS IN TENSION ABOUT SAID UNITS, SAID CASINGS AND SAID COLLAR MEMBERS BEING CONSTRUCTED OF GLASS. 